The present invention relates to a lever, having at least one connecting piece for connecting to the other parts of the mechanism.
Levers are used in a wide variety of forms for transferring force, for example in coupling mechanisms, pivoting levers, and as fastening levers for connecting to driven shafts. In motor vehicles, they are used among other things for driving windshield wipers. Frequently, they are constructed of a support profile that is U-shaped in the center which, on its flat ends, has connecting pieces in the form of sockets that are cast into bores by means of injection molding. The sockets are supported on a small surface which is essentially produced by the narrow wall thickness or material thickness.
Levers for windshield wipers are already known which are made of zinc or a zinc alloy by means of diecasting in a diecasting form (DE 44 44 328 A1). Each lever has a conical hub on its one end, which can be connected to a likewise conical axle. A reinforcing element is provided in the vicinity of the hub and is cast into the lever like a core. It is costly to manufacture levers of this kind.
The periodical xe2x80x9cWerkstatt und Betriebxe2x80x9d [Workshop and Operations], Karl Hanser Verlag Munchen, 1995, pp. 812 to 815 and the reprint from the periodical xe2x80x9cMetallumformtechnikxe2x80x9d [Metal Shaping Technology], Claus Dannert Verlag, 1994, under the title xe2x80x9cPrxc3xa4zisions-Werkstxc3xccke in Leicht-bauweise, hergestellt durch Innenhochdruck-Umformenxe2x80x9d, [Lightweight Precision Work Pieces Produced by Means of Internal High-Pressure Shaping] have disclosed a process for shaping pipes into work pieces. This process, which is primarily used for the automotive industry, works with high pressures.
The pipe section to be shaped is inserted into a split tool which has the desired work piece form incorporated into it. The tool, which is mounted in a press, is closed by means of a vertically functioning press ram. The pipe section ends are closed in a sealed fashion by means of closing tools through which a pressure medium is supplied which presses the pipe walls against the interior of the tool form. At the same time, horizontally acting rams exert an axial pressure onto the pipe section, which superposes the internal pressure. Consequently the material which is required for the shaping is not only taken from the wall thickness of the pipe section, but is also supplied by the shortening of the pipe. The closing tools are axially guided toward each other during the shaping.
According to the invention, the lever has a hollow profile made of material that can be the shaped without cutting, which on at least one end constitutes a receiving chamber for a prefabricated connecting piece. The walls of the receiving chamber rest tightly against the end faces and the circumference of the connecting piece so that it is encompassed by two opposing walls of the hollow profile in a secure, uniform, captive fashion. The contact faces between the walls of the hollow profile and the connecting piece are independent of the wall thickness and fulfill the requirements for a uniform force introduction and favorable force transfer. Furthermore, the connecting piece fits harmoniously into the contour of the lever.
Depending on function, the connecting pieces can be differently embodied so that a multitude of lever variants can be produced with the same hollow profiles and different connecting pieces. Thus, the connecting pieces can have a bearing bore for a pivoting bearing, a socket for a ball-and-socket joint, or threaded bore for a fastening screw. The bearing bore can also be used as a through bore for a fastening screw.
In order to enlarge the contact surfaces between the connecting piece and the walls of the hollow profile, it is suitable that the connecting piece has a collar against which the walls of the receiving chamber are pressed. The collar is simultaneously used for better alignment of the connecting piece to the hollow profile and gives it a more stable position. This is further encouraged by virtue of the fact that the thickness of the collar increases toward the outer circumference so that an undercut is produced toward the inside into which the walls of the receiving chamber are pressed.
In order to align the connecting piece before the pressing procedure and to secure it temporarily in the receiving chambers, it is suitable that the receiving chambers have pre-formed beads toward the center part of the hollow profile, against which the connecting piece can be laid and between which it can be slid or clamped with its collar.
According to other embodiments of the invention, form fitting elements are provided which produce a positive fit between the connecting piece and the receiving chamber in the circumference direction of the connecting piece. This is advantageously achieved by virtue of the fact that the connecting piece or its collar has one or a number of recesses on its end face or circumference, into which the walls of the receiving chamber are pressed or caulked. Furthermore, the cross sectional contour of the connecting piece can have a shape which diverges from that of a rotational body, for example a polygon or oval. In many instances, a flattening on the circumference sufficiently secures the connecting piece against rotation.
Depending on the intended use, it can be desirable that the connecting pieces are open toward both sides or only open toward one side. These two variants can be simply covered according to the invention by virtue of the fact that the receiving chamber of the hollow profile in one instance has two opposing connecting openings and in the other instance has only one connecting opening. In the second instance, largely closed and therefore protected pivoting bearings can be simply produced with the same connecting pieces.
The levers with a hollow profile have a greater torsional rigidity so that the wall thickness in relation to open profiles can be reduced while maintaining the same torsional and flectional rigidity. This results in a lower consumption of material and a reduced weight. Furthermore, sharp edges are largely prevented by means of the hollow profiles and therefore the danger of injury is practically eliminated.
The hollow profile is suitably produced using an internal high-pressure shaping process in which a pipe section is inserted into a split tool form and the pipe ends are closed by means of sealing tools. Then the tool form is closed and pressure fluid is supplied by way of the sealing tools, so that the internal contour of the tool form with the hollow spaces for the hollow profile with the receiving chambers is formed by means of the pressure increase. The pipe ends are suitably slid toward each other axially with the sealing tools. Consequently, an axial pressure is exerted on the pipe ends during the shaping and uniform wall thicknesses and precise contours are produced, which require little or no mechanical finishing work.
Then the part is removed from the tool form and the required connecting openings are let into it. After this, the connecting pieces are inserted into the receiving chambers and the walls are placed against the connecting pieces in particular by means of pressing or wobble forging. Wobble forging is a process in which a press tool executes a wobbling motion around the advancing axis during the pressing process, by means of which the pressing forces can be reduced.
The process according to the invention permits a flexible form embodiment so that even in a complex version, levers can easily be produced which make favorable use of the available space. Levers with a wide variety of hollow profiles both in the longitudinal direction and in the lateral direction can therefore be produced, which fulfill a wide variety of requirements with regard to space, torsional rigidity, flectional rigidity, and noise production in accordance with the intended use.
The process advantageously uses low-strength galvanized steel pipe or a pipe made of an aluminum alloy. They are sufficiently pourable and corrosion resistant and do not need to be subsequently treated. In addition, aluminum alloys also have other weight advantages. Both weld-free and longitudinally welded pipes are used.